Bug found
There's a problem editing expenses and deleting them (maybe also with incomes). I created the account zaj92907@ms9.mailslite.com for this example. It can be deleted when you want. All the images are here: https://docs.google.com/open?id=0B7hWWzROzzSWMmFhYzhhMWUtN2UyMC00ZDY0LWEzOGQtN2U2OTcxMjFhOGM1
Steps:
1. Add an expense of -2 $ (Image 1).
2. Edit the expense and change the value to 0 $ (Image 2).
3. Edit the expense again and change the value to -3 $. Now you just can see the income categories, but it is saved as expense.
4. There is a global value of 0 $ at @cash, instead of -3 $ (Image 3).
5. Delete the expense of -3 $.
6. There is a global value of 3 $ at @cash, instead of 0 $ (Image 4).